I started using this app a fe days ago and I'm already loving it. I've tried some other apps before and the complexity always was a frustration for me. Everyday resolves this by creating a simple product that allows me to track my habits in just two taps, therefore the rewarding feel is instantaneous. Regarding the overall design, it might not be visually stunning, but it responds to the app core values: pure functionality, therefore the current UI works.
The only stuff I think might be missing is the ability to create weekly habits. But I love its simplicity right now!